Shift control system of automatic transmission

Abstract

In a shift control system of an automatic transmission, wherein the shift control system includes at least a first and a second transmissions capable of automatically switching speeds separately of one another, and the first and the second transmissions are shifted simultaneously or alternately, to thereby achieve multi-speed shifts, there is provided means for starting and completing changes in rpm for the shift of rotary members of the second transmission during the operation of changes in rpm for the shift of rotary members of the first transmission, particularly when the first transmission is low gear shifted and the second transmission is shifted simultaneously, whereby the automatic transmission as a whole is down shifted, so that the shift characteristics can be maintained satisfactorily.

What is claimed is: 
     
       1. A shift control system of an automatic transmission, where said system includes at least first and second transmissions capable of automatically switching speeds separately of one another, said first and said second transmissions being capable of being shifted simultaneously, to thereby achieve multi-speed shifts, comprising: means for instructing said first transmission to switch speeds such that said first transmission is low shifted, whereby changes in rpm of rotary members of said first transmission subsequently occur;   means for judging said changes in rpm of rotary members of said first transmission; and   means for initiating rpm changes of rotary members of said second transmission in response to said judgment of changes in rpm for the shift of rotary members of said first transmission such that said first and second transmissions are shifted simultaneously and said automatic transmission as a whole is down shifted.   
     
     
       2. A shift control system of an automatic transmission as set forth in claim 1 including means for completing rpm changes of rotary members of said second transmission during operation of changes in rpm for the shift of rotary members of said first transmission. 
     
     
       3. A shift control system of an automatic transmission as set forth in claim 2, wherein said means for judging comprise a pressure switch adapted to be turned on when the hydraulic pressure of a frictionally engaging device associated with said shifts reaches a predetermined pressure. 
     
     
       4. A shift control system of an automatic transmission as set forth in claim 2, wherein said means for judging comprise means for determining whether or not a detected value reaches a predetermined value upon continuous detection of the hydraulic pressure of a frictionally engaging device associated with said shifts. 
     
     
       5. A shift control system of an automatic transmission as set forth in claim 2, wherein said means for judging comprise a timer for determining a lapse of time referenced from a time of judgment of said shift. 
     
     
       6. A shift control system of an automatic transmission as set forth in claim 2, wherein said means of judging comprise a timer for determining a lapse of time referenced from a time of command of said shift. 
     
     
       7. A shift control system of an automatic transmission as set forth in claim 2, wherein said means of judging comprise means for determining return of a piston of an accumulator of a frictionally engaging device associated with said shift. 
     
     
       8. A shift control system of an automatic transmission as set forth in claim 2, wherein said means of judging comprise means for determining a torque of an output shaft. 
     
     
       9. A shift control system of an automatic transmission as set forth in claim 2, wherein said means of judging comprise means for determining a change in rpm of an engine revolution speed. 
     
     
       10. A shift control system of an automatic transmission as set forth in claim 2, wherein said means of judging comprise means for determining a change in rpm of a specific rotary member in said automatic transmission. 
     
     
       11. A shift control system of an automatic transmission as set forth in claim 5, wherein said timer is set as commensurate to at least one of an engine load and vehicle speed. 
     
     
       12. A shift control system of an automatic transmission as set forth in claim 6, wherein said timer is set as commensurate to at least one of an engine load and vehicle speed.